A spark plug coil assembly has a primary core (26) bearing primary windings and a secondary winding spool (20) around which secondary windings are wound and in which the primary core (26) is received. A case (32) receives the spool (20) with core (26). The entire case (32) can be made of composite Iron to function as a magnetic return path for the core (26). Thick ends of the case (32) support the ends of the core (26).
